The counter-gravity casting process involves sealing a gas-permeable mold in the mouth of a vacuum chamber, immersing the underside of the mold in an underlying melt, and evacuating the chamber to draw melt up into the mold through one or more ingates in the bottom thereof. Such a process is exemplified by U.S. Pat. No. 4,340,108 wherein the melt is shaped in a resin-bonded-sand shell mold comprising cope and drag portions sealingly bonded together along a horizontal parting line lying outside the vacuum chamber (i.e., the vacuum chamber engages the cope). Such molds are susceptable to air infiltration at the parting line. Moreover, the outer surface of the cope, in its as-formed condition, is so rough as to make it practically impossible to seal to the mouth of the vacuum chamber. Accordingly, additional processing of the cope, after forming, has been required to flatten its upper surface sufficiently to effect a seal with the vacuum chamber.
It is an object of the present invention to provide an improved counter-gravity-casting, resin-bonded-sand, shell mold wherein the flat sealing surface of the mold adjoining the vacuum chamber is formed concurrently with the rest of the mold (i.e., without additional processing steps) and in such a manner that the molds parting line falls within the vacuum chamber.
It is a further object of the present invention to provide such an improved mold with a labyrinth seal at the parting line to prevent melt from escaping the mold into the vacuum chamber.